1. Field of the Invention
The present invention relates generally to medical devices and more specifically to disposable self-retaining laryngoscopes useful for orally intubating a patient with an endotracheal tube.
2. Background of the Prior Art
Laryngoscopes have long been used to open the mouth and airway to allow examination of the larynx and to assist in oral intubation of the compromised airway with an endotracheal tube.
To better understand the present invention, it is useful to review the prior art and the current state of the art in laryngoscopes. It is also necessary to understand why laryngoscope aided intubation is clinically important; why it is frequently difficult or impossible to accomplish with the prior art and to briefly discuss the consequences to the patient that can be caused by problems resulting from the use of prior art laryngoscopes.
U.S. Pat. No. 4,570,614, which issued to Bauman on Feb. 18, 1986, teaches a laryngoscope with a single disposable nonmetallic blade, a light source disposed within the handle and a light conductor disposed adjacent to and held by the blade. Typical of the prior art, this apparatus requires two hands to operate, and perhaps even two caregivers, if the patient's mouth and head must be stabilized. Lacy (U.S. Pat. No. 5,355,870) and Bar-Or et. al. (U.S. Pat. No. 5,702,351) also teach disposable plastic single blades used in combination with a light source in a laryngoscope.
U.S. Pat. No. 4,573,451, which issued to Bauman on Mar. 4, 1986, teaches a laryngoscope blade which has a tip that is capable being bent or flexed in the direction of the handle of the laryngoscope. This allows the patient's epiglottis to be lifted to expose the patient's larynx. This is a single blade instrument. It is provided with a ratchet lock to maintain the bend in the tip. This instrument can bend in only one direction, to lift the epiglottis. Locking the laryngoscope blade in an operable position is also shown in U.S. Pat. No. 5,651,760, but this lock/unlock mechanism functions to enable the instrument to be compact when it is not in use.
U.S. Pat. No. 5,036,835, which issued to Filli on Aug. 6, 1991, teaches a slideably adjustable spatula portion in the laryngoscope blade. The function of this spatula is to act as a tongue depressor to facilitate inspection of the pharynx and larynx, or the insertion of an anesthetic breathing tube. This apparatus uses a single blade with a sliding part, which does not lock in position.
U.S. Pat. No. 5,070,859, which issued to Waldvogel on Dec. 10, 1991, teaches a laryngoscope that incorporates a dynamometer in order to measure the force used by the caregiver to examine the patient. This invention is an attempt to avoid trauma to the patient that can occur using prior art apparatus.
U.S. Pat. No. 4,517,964, which issued to Upsher on May 21, 1985, teaches a dual bladed laryngoscope, wherein one conventional blade carries its own light source and the second blade is a light guide for a second light source in the handle of the instrument.
The closest prior art known to the present inventor is U.S. Pat. No. 5,498,231, which issued to Franicevic on Mar. 12, 1996. This apparatus is the current state of the art in the field of laryngoscopes. Franicevic teaches a reusable laryngoscope for use "in difficult intubation due to malformation of the jaws, tongue, pharynx, larynx or neck as a result of trauma, edema, inflammation or congenial anomalies." This laryngoscope has a hollow body terminating at its distal end in a pair of opposed blades that can be spread apart by the caregiver. An endotracheal tube slides through the hollow tube in the center of the instrument. Light conducting means are provided to illuminate the larynx. The device includes a fiberoptic optical system for inspecting the larynx during intubation. Franicevic is an improvement on the `bendable tip` of Bauman, cited above. The single distal spreading of the `beak` taught by Franicevic allows some lifting of the soft tissue, but it does nothing to open the mouth or depress the tongue. Franicevic teaches a bias spring to keep the distal blades closed when they are not positively spread apart by the caregiver. This apparatus is not locking or self-retaining in the airway. It also is not disposable and its complex mechanism makes it difficult to adequately sterilize.
Intubation using prior art laryngoscopes requires at least two hands. Four hands may be needed to hold the head and mouth of the patient, operate the laryngoscope and intubate the patient.
Prior art instruments are either reusable; and thus present risk of disease to the caregiver; or they use disposable single plastic blades, which become covered with blood and fail to light the airway. This can make it difficult or impossible to intubate the patient, even if the procedure is done in a hospital and the airway is normal. These problems become much more severe in the field; during emergency transportation of the patient; or when attempting to intubate an abnormal or damaged airway. When the prior art fails, effects on the patient are often severe. Respiratory related mishaps are a major source of patient morbidity and mortality. Should a difficult airway problem arise, approximately 40% will result in death, 20% in brain damage and 40% in high morbidity trauma. The incidence of difficulty in intubation is said to be between 1.2 and 2.5%, about 1 in 65 patients. This is a major medical problem, especially for the practitioner of emergency medicine. The number of different variations of laryngoscope found in the prior art is a good indication that many experts skilled in this art have tried to find solutions to these problems.
The causes of difficulty in endotracheal intubation are either congenital or acquired.
Congenital causes include conditions such as:
Pierre Robin syndrome. PA0 Cystic hygroma. PA0 Treacher-Collins syndrome. PA0 Gargoylism. PA0 Achondroplasia. PA0 Marfan's syndrome. PA0 excessive weight. PA0 short muscular neck and a full set of teeth. PA0 protruding incisors. PA0 long high arched palate with long narrow mouth. PA0 receding mandible. PA0 large swellings in the neck, mouth or upper chest. PA0 decreased distance between the occiput and the spinous process of C.1. PA0 increase in posterior depth of the mandible. PA0 increase in alveolar--mental distance requiring wide opening of the mandible. PA0 A. difficult blade insertion in the obese patient PA0 B. absence of any landmarks PA0 C. ineffective lighting PA0 D. inability to pass endotracheal tube PA0 A. hypoxia PA0 B. esophageal intubation PA0 C. glottic and epiglottic edema PA0 D. vocal cord injury PA0 E. tracheal perforation PA0 F. dental trauma PA0 G. endobronchial intubation PA0 H. pulmonary aspiration PA0 I. laryngospasm PA0 J. bronchospasm PA0 K. cervical spine injury PA0 L. increased intracranial pressure PA0 M. increased intraoculary pressure PA0 N. pulmonary edema
Numerous anatomical features have been identified that make endotracheal intubation difficult, especially in trauma patient who must be treated promptly in the field or during transport to a hospital. These include:
Endotracheal intubation using prior art laryngoscopes may also be difficult or impossible because of acute swelling in the neck due to trauma or bleeding. Intubation may be difficult if flexion of the neck is contraindicated because of cervical spine injury or severe rheumatoid arthritis.
The following categories of patients require a definitively secured airway:
1. Apnoea PA1 2. &lt;9 or sustained seizure activity. PA1 3. Unstable mid-face trauma. PA1 4. Airway injuries. PA1 5. Large flail segment or respiratory failure. PA1 6. High aspiration risk. PA1 7. Inability to otherwise maintain an airway or oxygenation.
The urgency of airway intubation is the most important factor in planning which technique of securing the airway is the safest and most appropriate. The caregiver must evaluate and assess the risk of further cord injury given head and neck movement, the degree of cooperation from the patient, anatomy and trauma to the airway and the caregiver's own expertise in each technique. Initially the airway should be cleared of debris, blood and secretions. It should be opened using the `chin lift` or `jaw thrust` maneuvers. The `sniffing the morning air` position for standard tracheal intubation flexes the lower cervical spine and extends the occiput on the atlas. An oral (Guedel) or nasopharyngeal airway may be necessary to maintain patency until a definitive airway is secured. Insertion of an airway produces minimal disturbance to the cervical spine. Bag and mask ventilation also produces a significant degree of movement at zones of instability.
The ATLS recommends a nasotracheal tube in the spontaneously breathing patient, and orotracheal intubation in the apnoeic patient. MANUAL in-line axial stabilization must be maintained throughout. The hard collar may interfere with intubation efforts and the front part may be removed to facilitate intubation as long as manual stabilization is in effect. Blind nasal intubation is successful in 90% of patients but requires multiple attempts in up to 90% of these. Nasotracheal intubation is (relatively) contraindicated in patients with potential basillar skull fracture or unstable mid-face injuries. In addition, it may produce hemorrhage in the airway, making other airway manipulations difficult or impossible.
Orotracheal intubation is generally accepted as the more usual method for securing the airway in the trauma patient. It is the fastest and surest method of intubating the trachea. At Shock Trauma in Baltimore, Md. (Grande C. M., Barton C. R., Stene J. K. "Appropriate Techniques for Airway Management of Emergency Patients with Suspected Spinal Cord Injury." Anesth Analg 1988;67:714-715) more than 3000 patients were intubated orally with a modified rapid sequence induction technique with pre-oxygenation and cricoid pressure. Ten percent of these patients were found to have cervical spine injury and none deteriorated neurologically following intubation.
Awake intubation is also a feasible option and is favored by some practitioners. It may be performed via the nasotracheal route, direct oral laryngoscopy or by fibreoptic technique. Successful fibreoptic tracheal intubation requires a cooperative patient, a secretion and blood free airway, a pharynx unrestricted by oedema and adequate supraglottic and infraglottic anesthesia. Such ideal conditions often do not exist, and local anaesthetic preparation of the airway is time consuming and might increase the risk of aspiration even if done in a proper hospital. Failed or difficult intubation is always a problem. Some nontramatic causes are:
Complications of direct laryngoscopy and intubation as taught by the prior art can be severe and can include:
In addition to these risks to the patient, most prior art laryngoscopes are reused. This is always true of complex designs, such as the laryngoscope taught by Franicevic, cited above. Such prior art laryngoscopes can present a risk of disease to the caregiver because they are often not possible to completely sterilize them after use. In most cases they are even not sterilized, but just washed by hand.